Effect of adsorption/coagulation on membrane fouling in microfiltration process post-treating anaerobic digestion effluent

Abstract

This study focused on reducing membrane fouling by adding different adsorbents (powder activated carbon (PAC), zeolite) or coagulants (polyamide, polyaluminum chloride) in a microfiltration process treating anaerobic digestion effluent. The results indicated that the magnitude of fouling reduction was highly associated with the type and dosage of adsorbents and coagulants. It was demonstrated that addition of reasonable doses of adsorbents/coagulants in the effluent of UASB could always lead to the alleviation of membrane fouling. Overdoses of PAC and zeolite could not benefit to reduce membrane fouling since they are potential to become foulants themselves through forming cake layer or blocking the membrane pores. Increasing dosage of polyaluminum chloride up to 100 mg/L could cause lower surface charge, which lead to dense deposit layer with less porosity on the membrane surface and accelerated the membrane fouling tendency. Polyaluminum chloride with a concentration of 10 mg/L was found most effective among the adsorbents and coagulants tested. Scanning electric microscope (SEM) photos further verified that mitigation of membrane fouling was associated with floc formation on the membrane surface through reduction of irreversible fouling. Therefore, air sparging would be employed with adsorbents/coagulants to further lessen membrane fouling by removing cake layer or inhibiting the formation of cake layer on the membrane surface.